In recent years, gene examination has rapidly spread in the field of clinical diagnosis. Gene examination is examination of the existence of mutations and karyotype's concerning genetic diseases for the clinical purpose by analyzing nucleic acids, chromosomes and the like. As an example of gene examination, there is an examination which determines whether or not a nucleic acid, derived from cancer cells, exists within a tissue excised from the living body. This examination process consists essentially of three primary steps: pretreatment, nucleic acid amplification, and detection.
Pretreatment step includes a variety of methods. By way of example, a reagent (buffer) for pretreatment is first added to cell mass such as lymph nodes, tumor mass and tissue fragments excised from the living body for the purpose of examination. Then, the excised tissue to which the reagent has been added is disrupted (homogenized), the resulting homogenate is centrifuged, and the target nucleic acid is extracted and purified, thereby giving a measurement sample. In the nucleic acid amplification step, the measurement sample is placed in a sample container, then reagents such as an enzyme, primers and the like are added thereto, and the target nucleic acid is amplified through the nucleic acid amplification reaction. In the detection step, the presence of the target nucleic acid in the excised tissue is judged or the concentration of the target nucleic acid is calculated, through measurements such as fluorescence measurement of the fluorescence-stained target nucleic acid or turbidity measurement of a by-product produced in proportion to the amplification.
In the gene examination described above, a variety of factors in each step affect the results of the measurement. Therefore, accuracy control for securing accuracy and reliability in each step is important in the field of gene examination. In the nucleic acid amplification step and in the detection step, accuracy control has been carried out by using a positive control and a negative control. In the pretreatment step, however, accuracy control has not been carried out.
Accordingly, the present inventors have previously proposed a substance for accuracy control, which can be used in accuracy control in pretreatment (US 2006/0084103). The substance for accuracy control in US 2006/0084103 is a pseudo-tissue for accuracy control comprising a nucleic acid or cells and a holding body that can hold the nucleic acid and cells. By using this pseudo-tissue for accuracy control, it becomes possible to conduct accuracy control in pretreatment of gene examination.
However, the substance for accuracy control in US 2006/0084103 has lower hardness than that of cell mass excised from the living body, and is thus easily disrupted and hardly exhibits the behavior of disruption similar to that of cell mass.